Hard-Disk-Drive Motor Controller from STMicroelectronics Designed for Next-Generation Enterprise Drives

Enterprise HDDs – typically used in server farms, workstations and high-performance desktop systems – are moving to Small Form Factor (SFF) sizes, where achieving a smaller PCB footprint is critical; the integration in the L7220 of the power FETs for both spindle and voice coil motors is a major contribution.

The new controller embeds four highly-efficient hysteretic positive switching regulators, and one -5V regulator, all with voltage margining. As well as eliminating the need for external regulators for the various voltages required by the drive, hysteretic control provides fast transient response and very high efficiency, increasingly important in server farms in particular, where reducing power consumption is a principal requirement.

In addition, the L7220 contains the latest version of ST’s respected Smooth Drive pseudo-sinusoidal digital-drive technique for minimizing acoustic noise from the spindle motor, plus other circuits to limit spindle current, sense the start-up position and slow the spindle during power down.

The spindle-motor section power FETs are capable of delivering 3.0A peak current; ON-resistance is 0.3-ohms maximum at 125 degrees C. The VCM driver has 2.5A capability and 0.3-ohms maximum bridge impedance. It includes circuitry for discontinuous mode ramp unload at power off, with end of travel detection; an alternative voltage-mode power-off scheme; and a 15-bit linear DAC with gain switch, for current commands.

Evaluation samples of the L7220 are available now, and volume production in planned for mid-2008.